Sample 'eu.gcr.io' registry secrets usage with "balena build"

Dockerfile

FROM eu.gcr.io/buoyant-idea-226013/arm32v7/busybox
RUN uname -a
CMD while : ; do echo "(Plain Dockerfile 3) $(uname -a)"; sleep ${INTERVAL=5}; done

sample_secrets.yml

'eu.gcr.io':
    username: _json_key
    password: '{
  "type": "service_account",
  "project_id": "buoyant-idea-226013",
  "private_key_id": "454ddbbe3b6b31f50dde337f3fed8025871c5b6e",
  "private_key": "-----BEGIN PRIVATE KEY-----\nA+LONG+PRIVATE+KEY+STRING\nWITH+ESCAPED+LINE+BREAKS+AND\NMORE+THAN+A+THOUSAND+CHARACTERS=\n-----END PRIVATE KEY-----\n",
  "client_email": "container-registry-test@buoyant-idea-226013.iam.gserviceaccount.com",
  "client_id": "107317699110545445744",
  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
  "token_uri": "https://oauth2.googleapis.com/token",
  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
  "client_x509_cert_url": "https://www.googleapis.com/robot/v1/metadata/x509/container-registry-test%40buoyant-idea-226013.iam.gserviceaccount.com"
}'

shell command

DEBUG=1 balena build -a test-project --registry-secrets sample_secrets.yml .

• Note the escaping of line breaks in the "password" field of the sample_secrets.yml file above. (By the way, the "private key id" and "private key" fields have been modified: not real values, just a sample.)
• The 'eu.gcr.io' value must match between the Dockerfile FROM line and the key entry in the sample_secrets.yml file.